1. Field of the Invention
This invention relates to the field of ultrasonic flow meters, for determining the rate of flow of a fluid in a conduit. More particularly, this invention is related to means and method for determining the flow rate more precisely than has been possible in the past.
2. Description of the Prior Art
A convenient and commonly used means of measuring fluid flow is by the use of sonic flow meters. These are devices which transmit sound pulses or wavelets through the fluid flowing in a conduit. In the most commonly practiced means of employing ultrasonics for measuring fluid flow rate, an ultrasonic path is provided between an upstream and downstream location, spaced on opposite sides of a conduit. The rate of travel of the sound through the liquid is measured in both directions, that is, with the liquid flow direction against the sonic flow, and the other direction where the liquid flow direction and the sonic flow direction are the same. In the preferred method for practicing the invention, the rate of travel of the sound through the liquid is measured in both directions, that is, with the fluid component direction with and against the fluid flow component. By subtracting such measurements which effectively cancels out the rate of sound flow upon travel through the fluid itself, the rate of fluid flow can be accurately determined.
There have been a number of prior art patents describing such systems, mainly with the point of view of correcting for temperature or viscosity or other variables which would affect the precision of the measurement.
In this invention the emphasis is placed on the method of measuring time intervals precisely, so that the most accurate value of velocity can be determined.